1. Field of the Invention
The subject invention relates to an apparatus for activating and deactivating a wedge clamp on a circuit card and to facilitate extraction of the circuit card from an electrical apparatus.
2. Description of the Prior Art.
Prior art electrical and electromechanical apparatus include circuit boards to which a plurality of circuit cards are connected. Electrical components and circuitry on the circuit card may be required to supplement or control functions enabled by circuits and components on the circuit board. However, the circuit card must be removably engageable with the circuit board to enable replacement of damaged components or to alter the performance of the apparatus.
Circuit boards with circuit cards removably connected thereto often are used in high-vibration environments, such as on aircraft and in some land vehicles. Vibrations can cause the circuit card to vibrate free of its electrical connection with the circuit board. An unintentional separation of a circuit card from a circuit board can have a catastrophic effect on the performance of the apparatus in which the electrical circuitry is disposed.
The prior art has recognized a need to securely, but releasably, clamp a circuit card into an electrically connected condition on a circuit board. A prior art electrical apparatus with a circuit board and a clampingly engageable circuit card is illustrated schematically in FIGS. 1 and 2 and is identified generally by the numeral 10. The prior art apparatus 10 includes a circuit board 12 having a substrate 14 with an array of circuits printed or otherwise disposed thereon. Electrical components will be connected to conductive traces on the substrate 14 in accordance with the function to be performed by the apparatus 10. The circuitry and electrical components do not form a part of the subject invention, and are not illustrated in FIGS. 1 and 2.
The circuit board 12 further includes at least one socket 16 mounted to the substrate 14. The socket 16 includes a plurality of apertures 18 and a corresponding plurality of electrically conductive terminals (not shown) mounted therein. Each terminal will include a contact portion aligned with the corresponding aperture 18 and a solder tail, or other such member, for soldered electrical connection to an appropriate conductive trace on the substrate 14. The prior art circuit board 12 further includes a chassis 20 having pairs of spaced apart parallel front and rear clamping walls 22 and 24 and an end wall 25 projecting rigidly from the substrate 14 and defining a card receiving channel 26 therebetween.
The prior art apparatus 10 further includes a circuit card 28 having a substrate 30 with electrically conductive circuits and components thereon to supplement the circuits and components of the circuit board 12. The circuit card 28 further includes a multi-terminal plug 32 having a housing 34 mechanically mounted to an edge region of the substrate 30. A plurality of electrically conductive terminals are mounted in the housing 34 and include contact pins 36 which project from the housing 34 of the plug 32. The terminals of the plug 32 are electrically connected to circuitry on the card 28 by leads illustrated schematically in FIG. 1 and identified generally by the numeral 38. The pins 3 of the plug 32 are disposed and dimensioned to enter the apertures 18 of the socket 16 and make electrical contact with the terminals thereof.
The apparatus 10 further includes a pair of prior art wedge clamps 40 mounted to opposed edges of the substrate 30. The prior art wedge clamp 40 includes a plurality of generally prismatic wedges 42, 44 and 46 having opposed faces disposed in sliding contact with one another. A threaded screw extends through the wedges 42-46 and include a head 48 dimensioned and configured to be engaged by a prior art Allen wrench 50, as shown schematically in FIG. 2. In a loosened condition, the side faces of the prismatic wedges 42-46 will be generally registered with one another and in common respective planes. In this loosened condition, the circuit card 28 and the prior art wedge clamp 40 can be slid easily into the channel 26 defined between the front and rear clamping walls 22 and 24. The prior art Allen wrench 50 then can be engaged with the head 48 to tighten the screw. As illustrated in FIG. 2, this tightening causes the prismatic wedges 42 and 46 to slide toward one another and along the opposed end faces of the prismatic wedge 44. This effectively increases a cross-sectional dimension of the prior art prismatic wedge 40 and causes the substrate 30 and the prior art wedge clamp 40 to be tightly clamped between the front and rear clamping walls 22 and 24 of the chassis 20 as illustrated in FIG. 2.
The prior art apparatus 10 with the prior art wedge clamp 40 as shown in FIGS. 1 and 2 has worked successfully for releasably clamping a prior art circuit card 28 in a connected condition relative to a circuit board 12. However, the clamping and unclamping of the circuit card 28 relative to the circuit board 12 requires the technician to have access to an appropriately dimensioned Allen wrench 50. The availability of the required Allen wrench may not be a problem in a well appointed laboratory or work shop. However, circuit card replacements often are made in the field where the technician cannot be assured of access to the required tools. The technician may resort to merely sliding the prior art circuit card 28 into connection on the circuit board 12 without activating the wedge clamp 40. Hence, the circuit card 28 will be susceptible to unintended separation when exposed to a high vibration environment.
To remove the prior art circuit card 28 from the circuit board 12, the prior art wedge clamp 40 must be loosened and a pulling force must be exerted on the circuit card 28. The pulling force is required to overcome the contact forces between terminals in the socket 16 and the pins 36 in the plug 32. The contact forces between each pair of mated terminals is fairly low and can be overcome easily with a simple application of manual force. However, the connectors 16 and 32 are likely to have a large number of mated terminals (e.g., 64 mated pairs) and the unmating forces for the circuit card 28 is the sum of the unmating forces required for each pair of mated terminals. These combined unmating forces can be very high, and may require the technician to use a separate extraction tool. As noted above, a technician working in the field cannot be assured of having full access to available tools. Improper application of forces on a circuit card by using either the wrong tool or no tool at all can damage either the circuit card 28 or the board 12.
In view of the above, it is an object of the subject invention to facilitate the clamped retention of a circuit card to a circuit board.
It is another object of the subject invention to facilitate the extraction of a circuit card from a circuit board.
It is a further object of the subject invention to avoid the need for separate tools to insert or extract a circuit card from a circuit board.